Electrolytic cell having self-aligning anodes

ABSTRACT

This invention provides an improvement in electrolytic cells of the type having a porous diaphragm separating the anode and cathode of each unit cell and having a space between the anode and the porous diaphragm. Such electrolytic cells are used for the manufacture of hypochlorite or the production of chlorine and caustic alkali. Particularly, the improvement relates to minimizing the distance between the anode and cathode required for assembling the cell while maintaining a uniform gap between the anode and the diaphragm. The anode mounting assembly includes threaded studs which have a smaller diameter than the holes in the base plate though which the studs project, such that when the anodes are loosely held on the base plate, they can be self-aligned horizontally when a cathode is inserted between each pair of anodes.

March 12, 1974 F. E. CONNER, JR ETAL 3,796,648

ELECTROLYTIC CELL HAVING SELF-ALIGNING ANODES Filed Dec. 22. 1971 2 Sheets-Sheet l I-LJ rl-L. 1-11 FIG.2

ELECTROLYTIC CELL HAVING SELF-ALIGNINGANODES Filed Dec. 22, 1971 2 Sheets-Sheet 2 RUN A RUN B AMPERAGE O.I25 AVERAGE 32.6 VOLTAGE REDUCTION 3,2 0 I I I I I I I ANODE TO CATHODE VOLTAGE (VOLTS) ),United States Patent O 3,796,648 ELECTROLYTIC CELL HAVING SELF- ALIGNING ANODES Frank E. Conner, Jr., Charleston, Terry Fontalhert, Marmet, John W. McFarland, Charleston, and Don W.

Lewis, Nitro, W. Va., assignors to FMC Corporation,

New York, N.Y.

Filed Dec. 22, 1971, Ser. No. 210,991 Int. Cl. C23b 5/68 U.S. Cl. 204-286 2 Claims ABSTRACT F THE DISCLOSURE This invention provides an improvement in electrolytic cells of the type having a porous diaphragm separating the anode and cathode of each unit cell and having a space between the anode and the porous diaphragm. Such electrolytic cells are used for the manufacture of hypochlorite or the production of chlorine and caustic alkali. Particularly, the improvement relates to minimizing the distance between the anode and cathode required for assembling the cell while maintaining a uniform gap between the anode and the diaphragm. The anode mounting assembly includes threaded studs which have a smaller diameter than the holes in the base plate through which the studs project, such that when the anodes are loosely held on the base plate, they can be self-aligned horizontally when a cathode is inserted between each pair of anodes.

This invention concerns electrolytic cells of the Hookertype which consist essentially of a cell enclosure, an anode of chlorine-resistant electroconductive material, such as carbon, platinum or platinum coated titanium, a foraminous cathode, usually made of iron and a porous diaphragm of asbestos or like material which is placed in the anode-cathode gap to provide an anode compartment and a cathode compartment. f

In the normal construction of such cells, the diaphragm is in direct contact with the cathode. Frequently, the diaphragm is deposited on the cathode by placing the cathode in an aqueous slurry of asbestos and causing the slurry to ow through the pores or mesh openings of the cathods until a porous sheet or layer of asbestos has been deposited upon the side of the cathode which in use is opposite the anode.

-Electrolytic cells employing a porous diaphragm between the anode and cathode are widely used in the production of chlorine and caustic alkali by the electrolysis` of an alkali metal chloride solution. Generally, all diaphragm cells for the production of chlorine and caustic alkali can be divided into two types:

(l) Bipolar cells such as the cell described in U.|S. Pat. 3,242,059 in which both the anode and cathode contact the diaphragm (no gap between anode and diaphragm), and

(2) Conventional or Hooker-type cell, that is the diaphragm cell in which a gap is maintained between the anode and the diaphragm. As used herein, the term Hooker-type cell, refers to all conventional type diaphragm cells.

In the `Hooker-type cell, the anode is usually graphite or a dimensionally stable metal electrode and the cathode is usually foraminous iron or steel. The cells contain a plurality of anodes and cathodes. The anodes are fixed to a cell base and are spaced apart so that the cathodes can be alternated between the anodes.

lAn alkali metal chloride solution is used in the cell as the electrolyte. As current is passed through the electrolyte between the anode and cathode, chlorine is evolved at the anode and alkali metal ions are discharged 3,796,648 Patented Mar. l2, 1974 at the cathode which ions react at the cathode base with water from the electrolyte to form caustic alkali and liberate hydrogen. A porous diaphragm is placed in the anode-cathode gap in order to prevent as far as possible. mixing of the hydrogen with chlorine and mixing of the caustic alkali with the incoming brine which is fed to the anode side of the diaphragm.

In the Hooker-type cells, it is desired to keep the anode-cathode gap small since the resistance of the electrolyte in the gap to the passage of the electrolyzing current raises significantly the operating voltage of the cells and consequently increases the energy consumption and decreases power etliciency.

With Hooker-type diaphragm cells the anode-cathode gap cannot be reduced below a certain minimum distance. During operation of the cell as a chlorine cell, a minimum gap between the anode and the diaphragm is required both for passage of chlorine that is evolved at the anode and to replenish the brine solution in contact with the anode. If this gap is too small then during operation of the cell the diaphragm becomes ineffective due to insufiicient brine flow, the formation of gas pockets or hot spots. Furthermore, additional space is required during assembly of the cell, between the anode and the cathode to prevent scraping between them caused by dimensional deviations or misalignments of the anodes and cathodes. Although a minimum gap is needed during operation of the Hooker-type diaphragm cell, the size of the gap was dictated by the space required between the anode and cathode during assembly of the cell to prevent scraping between them during assembly. Scraping between the anode and cathode must be avoided because it results in breaking of the diaphragm which causes operating problems due to mixing of the anodic and cathodic products.

lDespite the problems that may occur when the gap between the anode and diaphragm is reduced, commercial installations attempt to minimize the gap between the anode and diaphragm because reduction of this gap results in considerable savings in energy consumption due to the reduction in the resistance to current flow and concurrent lowering of cell voltage.

When a Hooker-type cell is assembled containing a plurality of fixed anodes arranged vertically in a regular pattern with spaces between each anode and a corresponding pattern of iixed cathode lingers which fit between the spaces of the anodes, the minimum gap between the anode and cathode is usually approximately 1V: inch in commercial installations. 'This gap is mainly required to allow for misalignment or dimensional irregu-` larities of the anodes and cathodes. These misalignments and dimensional irregularities are caused by dimensional tolerances in constructing the anode and cathode assem blies and subsequent dents, deformities or warping in the cathode lingers or dimensionally stable anodes which occur during assembling and disassembling of the cells despite great care.

Although gaps of less than 1/2 inch between the anode and the diaphragm would be adequate for cell operation (provide for chlorine flow and replenishment of the brine), the magnitude of the minimum gap in commercial installations of about 1/2 is required to prevent the anode and cathode assemblies from scraping against each other during assembly which scrapes off the diaphragm formed on the cathode. Even with a gap of about 1/2 inch, great care is required in lowering the cathode assembly between the anodes which is diicult and time consuming and thereby raises the cost of assembly.

This invention described in summary form provides a novel self-aligning multiple anode structure and a method of assembling a Hooker-type diphragm cell preferably employing the novel multiple anode structure which significantly reduces the gap required between the anode and the cathode. The novel anode structure comprises; a base plate, a plurality of essentially parallel dimensionally stable metal anodes, said anodes having anode mounts for attaching the anodes in an essentially perpendicular position to the base plate and said anode mounts having means to provide two modes of attaching the anode to the base plate, a first mode in which the metal anode is moveably attached to the base plate permitting selfaligning, horizontal movement of the anodes in relation to the base plate, and a second mode in which the metal anode is rigidly attached to the base plate preferably in its self-aligned position.

This invention also provides an improved method of assembling a Hooker-type diaphragm cell characterized by having a cell can, a cell base plate, an anode of chlorine-resistant electroconductive material, a foraminous cathode, a porous diaphragm on the cathode surface and a gap between the anode and the diaphragm, wherein the improvement comprises the following steps:

(a) Mounting the essentially vertical and parallel anodes to the essentially horizontal cell base plate;

(b) Positioning the cathode for insertion between the anodes;

(c) Before inserting the cathodes interposing smooth essentially vertical guiding and spacing members between the anodes and the diaphragm surface on the cathodes; and

(d) Inserting the essentially vertical cathodes having the diaphragm surface between the anodes whereby a minimum gap is obtained equal to the thickness of the guiding and spacing members and whereby misalignment of the anodes with respect to the cathodes is corrected by horizontal movement between the anodes and the cathodes. In a preferred embodiment the anodes are urged into aligning horizontal movement during assembly with the cathode by sliding contact at points of misalignment between the spacing members and either the anodes or the diaphragm surface on the cathodes. Steps (c) and (d) could be performed simultaneously by placing the spacing members on either the anodes or cathodes before assembly (after step (a)) whereby the spacing members become interposed between the anodes and cathodes simultaneously with the insertion of the cathodes.

FIG. 1 is a simplified side view of the novel anode structure.

FIG. 2 is a simplified side view of a typical Hookertype diaphragm cell partially assembled with the cathodes in a partially inserted position, and with the cell can be removed for clarity.

FIG. 3 graphically depicts the improvement in voltage drop obtained with this invention.

Specifically this invention provides a novel multiple anode structure for a Hooker-type diaphragm cell and an improved method of assembling a Hooker-type diaphragm cell of the type having a cell base, a cell can, anodes and diaphragm coated cathodes.

The novel anode structure comprises (a) a supporting cell base means preferably having holes therein for receiving anode mounts, (b) dimensionally stable metal anodes, said anodes preferably having an electrically conductive surface, material supporting said conducting surface, and an anode mount preferably extending through the cell base, said mounts being adaptable to two modes, a first mode in which the anode is free to move parallel to the plane of the cell base and a second mode in which the anode is fixed to the cell base.

The interrelationship between the structural configuration of the anode mounts and the cell base must be such that the anode mounts can move laterally with respect to the cell base when the anode mount is in a first mode and the anode mount must be fixed to the cell base to prevent lateral motion when the anode mount is in the second mode. When the anode mount is in the first mode, the anode should be free to move at least 1,@,2 of an inch and preferably about 1A inch.

With reference to FIG. l, this interrelationship between the structural configuration of the anode mounts and the cell base is preferably obtained as follows: (a) a cell base plate 10, having disposed herein a number of holes 12, through which anode mounts 14 protrude, (b) the anode mount 14, is a stud having a diameter sufficiently smaller than the hole 12, in the cell base plate 10, to permit about A inch lateral movement of the anode 16, attached to the stud, and (c) a nut 18, larger than the hole in the cell base plate is threaded onto the end of the stud 1, protruding through the hole. A washer 20, is usually inserted between the nut 18, and the cell base plate 10. A collar 21 to facilitate sliding of the anode is preferably attached to the stud above the base plate. The first mode is achieved with the nut 18, loosely threaded onto the stud 14, to permit lateral sliding of the stud in the hole. The second mode is achieved by tightening the nut to secure it against the base plate.

It should be understood that the novelty of the instant invention does not reside in the design and construction of an anode surface, a diaphragm, the cathode or the cell can. Any of the constructions currently in use are acceptable and may be adapted to the present invention. The type of construction embodied in U.S. Pat. 2,987,463 is typical of the type of cell construction commercially used wherein the cathodes are in the form of parallel hollow fingers projecting horizontally from the two opopsite sides of the cell can and are adapted to alternate with the anodes. The diaphragm in this type of operation is deposited upon the perforated or foraminous cathode material itself.

IMovement between the anode and the cathode results in self-alignment of the anodes and cathodes in the cell structure which permits a decreasing of the gap between the anode and the cathode with its resulting voltage drop and improved eiciency for cell operation. When the cell is assembled employing both the novel anode structure and the improved method of assembly, the minimum gap between the anode and the diaphragm is the gap required for efficient cell operation (space for escaping chlorine and replenishing the brine) rather than the previously larger gap required for assembly of the cell.

The minimum gap required for operation of the electrolytic cell depends upon the specific design of the cell and contemplated operating conditions. However, a gap between the anode and diaphragm of less than 1/16 of an inch would tend to be impractical while a gap of about 1/2 inch would approach the prior art minimum obtainable gap without the self-aligning ability provided by this invention. The preferred gap between the anode and the diaphragm is about 1A inch, which can be accurately obtained by employing 1A inch spacing members. Such a cell having the preferred M1 inch gap has an extremely low resistance to the passage of electrolyzing current, may be assembled and disassembled rapidly with good dimensional accuracy, may be operated at higher current densities, yields greater cell power and current eiciency.

The structural characteristics of conventional foraminous metal cathodes permit some flexing or horizontal movement of the cathode fingers. Therefore, self-aligning horizontal movement between the anode and the cathode during assembly of a Hooker-type cell having fixed anodes can be obtained by employing the novel guiding and spacing members to urge the cathode fingers into alignment without scraping off the diaphragm. The cathode structure could be modified to permit horizontal movement to facilitate alignment. However, alignment is preferably obtained with less difficulty and less force required to produce the aligning movement between the anode and the cathode when both the novel self-aligning anode structure and the novel spacing and guiding members are used in assembling the cell.

Self-aligning movement between the anode and the cathode is preferably obtained during assembly of the cell by the sliding contact between the spacing members and either the anodes or the diaphragm surface of the cathodes. However, when the novel self-aligning anode structure is used, the movement between the anodes and cathodes can also be obtained by applying a force directly to the anode mounts or by the use of mechanical linkage or its equivalent, to physically adjust the alignment of the anode after or during assembly of the anodes and cathodes.

Many types of dimensionally stable anodes for which this invention is useful are known in the art. A typical one is described in U.S. Pat. 3,591,483. The configuration and designs of the dimensionally stable anodes to be used with the present invention can be any of a number of variations generally known in the art in that essentially all dimensionally stable anodes are operable in the present invention.

The dimensionally stable anodes which are preferred in the practice of the present invention comprise an electrically-conductive surface, a material supporting said electrically-conductive surface and an anode mount in contact with the material which supports the electricallyconductive surface, for mounting the anode to the cell base plate. The electrically-conductive surface of the dimensionally stable anodes may be composed of any material which has a sufiiciently low chlorine overvoltage and which is chemically inert to the electrolyte as well as resistant to the corrosive conditions of the cell. Typically this electrically-conductive surface will be composed of platinum group metals, alloys of platinum group metals, platinum group oxides, mixtures of platinum group oxides and alloys which are mixtures of platinum group metal oxides with platinum group metals.-

The material which supports the electrically-conductive surface generally comprises film-forming metals such as titanium, tantalum, zirconium, niobium and the like. This material can be in the form of a continuous sheet of metal or preferably in the form of perforated or foraminous metal in order to provide circulation of the anolyte. These film-forming metals have in common the property of being non-conductors themselves under the conditions of cell operation (in oxide of the metal quickly forms on the surface thus preventing passage of current, but being able to conduct current when an electricallyconductive material is in contact with a portion of the surface of the film-forming metal.

The material which supports the electrically-conductive surface is in contact with the anode mount, generally by welding. This mount serves to dispose the anode in the proper manner within the cell and to convey electric current to the anode surface. The mount is preferably constructed, at least on the outer portions thereof, of a Ifilm-forming metal such as titanium or tantalum. As an alternative to u sing a mount consisting of solid filmforming metal, it is possible to use a copper or aluminum cored mount having a layer of film-forming metal on the outside. This is preferable because copper or aluminum are less expensive and are better conductors of electricity than the film-forming metals.

The novel anode structure is not dependent upon the particular structural or surface characteristics of individual dimensionally stable anodes employed in making the anode structure, but the novelty resides in providing selfaligning horizontal movement of thev anodes with respect to the cell base either during or after assembly.

During assembly of the cell the novel guiding and spacing members perform four functions (1) guide the cathode between the anodes during assembly, (2) transmit a force between the anode and the cathode during assembly which results in self-aligning movement between the anode and cathode without abrading the diaphragm, (3) minimize the gap between the anode and cathode to reduce electrical resistance, and (4) maintain a minimum gap between the anode and the diaphragm which prevents contact between the diaphragm and the anode and provides an escape passage for chlorine evolved at the anode.

The spacing member should be constructed of material that s essentially non-conducting under the conditions of operation of the cell or if constructed of a conducting material it must be removed after assembling the anodes and cathodes but prior to operating the cell. The spacing members must be interposed between the cathodes and anodes for at least until the anodes and cathodes are assembled and aligned with respect to each other. Preferably the guiding and spacing members are removed after the cell is assembled.

Spacing members are preferably constructed of cylindrical, smooth, non-conducting material shaped in the form of a candy cane with the curved part fitting over the anode or under the cathode. The preferred thickness for the spacers is between M6 inch and inch with A inch being particularly preferred.

The preferred materials of construction of the spacing member are plastic (such as polypropylene or polyvinyl chloride), hard rubber, Teflon or other materials that are inert in the electrolytic solution. (Teon is particularly preferred.) Although inert material is preferred for the spacing member, material that decomposes during cell operation is not objectional if the decomopsition products do not interfere with the operation of the cell.

The best mode contemplated of practicing this invention is depicted in FIG. 2. With reference to FIG. 2, the improved method of assembling a Hooker-type diaphragm cell employing the 4novel self-aligning anode structure comprises (a) Constructing the novel self-aligning anode structure by mounting essentially vertical dimensionally stable anode 16 to an essentially horizontal cell base plate 10 by inserting anode mounts 14 through cell base plate holes 12A and loosely threading anode retainer nuts 18 onto the anode mounts along with washer 20 below the base and collar 21 with gasket 22 above the base (the anode retainer nut being loose results in the first mode for the anode mount which permits horizontal movement of the anode and anode mount with respect to the cell base plate);

(b) Placing the candy cane shaped l1/4 inch diameter Teflon guiding and spacing members 24 over the anodes;

(c) Lowering the cathode assembly 26 between the anode structure which results in the sliding contact between the guiding and spacing members and the cathodes to cause self-aligning movement of the anodes;

(d) Tightening the anode retainer nuts 18 to fix the anodes in their aligned position;

(e) Removing at least some of the guiding and spacing members; and

(f) Completing the assembly of the Hooker-type diaphragm cell according to conventional means.

EXAMPLE Run A-This invention A Hooker-type diaphragm electrolytic cell was constructed with 1.5 inch wide self-aligning dimensionally stable metal anodes and cathodes having about 2% inch spaces between cathode fingers. Smooth polypropylene spacers having a 1% inch diameter circular cross-section and bent into form of -a U Iwere placed over the anodes. The cathode fingers were coated with a porous asbestos diaphragm and were inserted between the anodes. This resulted in sliding contact between the spacing members and the diaphragm surface on the cathode which caused the anodes to align themselves with a V4 inch gap being maintained between the anode surface and the diaphragm (a 5/16 inch gap between anodes and cathodes). -During assembly of the anodes and cathodes the anodes were loosely mounted on a cell base plate to permit horizontal movement of the anodes parallel to the base plate. After assembly of the anodes and cathodes the anode mounts were secured to prevent horizontal movement of the anodes which fixed the anodes in their self-aligned position. Most of the spacers were then removed between the anodes and cathodes, however, spacers maintaining the '1A inch gap at points of significant misalignment were tightly wedged in position and were not removed. The assembly of the cell was completed according to conventional means and the cell was operated to produce chlorine, caustic alkali, and hydrogen according to conventional methods. The cell was operated for months and the voltage drop across the cell monitored. The results are reported in FIG. 3.

Run B-Prior art A conventional electrolytic cell was constructed similar to the cell in Run A except that the guiding and spacing members were not used during assembly and fixed anodes were employed having a maximum practical width of 1.275 inches. A width greater than this would result in excessive abrasion and contact between the anodes and the diaphragm during assembly. This cell was also operated for months to produce chlorine, caustic alkali, and hydrogen under identical operating conditions (same circuit and time) as the cell operated in Run A except that in order to maintain equivalent production rates the voltage drop across the cell of Run B was greater than the voltage drop across the cell of Run A. The voltage drop across the cell was monitored and is reported in FIG. 3.

What is claimed is:

1. A multiple anode assembly for a Hooker-type diaphragm cell comprising a base plate and a plurality of essentially parallel dimensionally stable metal anodes, said anodes having anode mounts for attaching the metal anodes in an essentially perpendicular position to the base plate in which:

the base plate has a plurality of holes; the anode mounts are threaded studs protruding through said holes having a diameter at least %2 inch smaller than said hole and having a nut on the end of the stud protruding through said holes;

said anode mounts providing two moles of attaching the anodes to the base plate, said first mode being achieved with the nut loosely threaded onto the stud and the second mode being achieved with the nut tightly threaded onto the stud and secured with respect to the base plate.

2. An improved method of assembling a Hooker-type diaphragm cell characterized by having a cell can, a cell base plate, an anode of chlorine-resistantelectro-conductive material, a foraminous cathode, a porous diaphragm on the cathode surface, and a gap between the anode and the diaphragm wherein the improvement comprises the following steps:

(a) mounting the essentially vertical and parallel anodes to the essentially horizontal cell base plate so that the metal anodes are moveably attached to the cell base to permit self-aligning horizontal movement of the anodes in relation to the cell base plate;

(b) positioning the cathodes for insertion between the anodes;

(c) before inserting the cathodes interposing smooth essentially vertical guiding and spacing members between the anodes and the diaphragm surface on the cathodes;

(d) inserting the essentially vertical cathodes having the diaphragm surface between the anodes whereby a minimum gap is obtained equal to the thickness of the guiding and spacing members, and whereby misalignment of the anodes with respect to the cathodes is corrected by horizontal movement between the anodes and the cathodes;

(e) rigidly attaching the metal anodes to the cell base plate; and

(f) removing at least one of the guiding and spacing members.

References Cited UNITED STATES PATENTS 3,498,903 3/1970 Kamarjan 204-286 3,591,483 7/l97l Lofteld et al 204--252 3,579,431 5/1971 Jasberg 204-280 3,674,676 7/ 1972 Fogelman ZOLL-252 JOHN H. MACK, Primary Examiner W. I. SOLOMON, Assistant Examiner U.S. Cl. X.R. 204-252, 266

UNITED STATES PATENT OFFICE CERTIFICATE 0E CORRECTION Patent Nm 3,796,6118 March 12, 19714 y Dated Inventor(s) Fn En LT1/0, als

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line ll, "l" should read ll.

Column 5, line 12, "current" should read --current).

Column 7, line 39, "moles" should read --modes-f.

Signed and sealed this lOthvday of June 1975.

(SEAL) Attest: y

C. MARSHALL DANN RUTH C. I-IASON Commissioner of Patents Attestng Officer and Trademarks 

